There have been known glycosaminoglycan-bonded substances formed by binding various substances (for example, proteins, phospholipids, lipids and the like) to a hemiacetal of a reducing end sugar of a glycosaminoglycan optionally activated. Attempts have been made to apply these substances to drugs (JP-A-3-284698 corresponding to EP-A-454898, International Publication No. WO92/01720 corresponding to EP-A-493622; the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Also, slight changes in the amount or microstructure of glycosaminoglycans have attracted public attention with regard to the infection with bacteria or viruses, cancer, hereditary diseases, etc. These changes frequently depend on glycosaminoglycan-degrading enzymes occurring in a trace amount in cells, tissues and body fluids. Accordingly, it has been regarded as important to assay these enzymes.
It is not suitable for assaying glycosaminoglycan-degrading enzymes to use such a method as those employed in assaying glycosidase, i.e., one comprising using a substrate consisting of a monosaccharide or an oligosaccharide and a chromogenic compound or a fluorescent compound bonded thereto and observing and measuring the rate and the manner of appearance or disappearance of the color development (or fluorescence) due to the digestion with the enzymes. Thus, these enzymes have been assayed by using a glycosaminoglycan as a substrate and determining the disaccharide or oligosaccharide formed by digestion or examining a decrease in the molecular weight. There has been known a gel electrophoretic method for assaying a protease or the like which is called "zymography" and comprises electrophoresing an enzyme on a gel having a substrate uniformly embedded therein and, after the digestion of the substrate with the enzyme, measuring the loss in the substrate. In this method, however, high molecular weight compounds are exclusively usable as the substrate, since a low molecular weight substrate per se would be electrophoresed and thus flow out from the gel. Moreover, these methods are disadvantageous in that a complicated operation is required, sensitivity and reproducibility are poor and applicable substrates are limited.